The present invention relates to a slit scanning exposure apparatus suitable for use with various types of copiers, printers, presses, etc. More specifically, the present invention relates to a slit scanning exposure apparatus that is capable of effective light adjustment, in particular, the adjustment of the quality of light by means of color filters, with satisfactory color and density reproduction. The present invention further relates to a slit scanning exposure apparatus that is capable of preventing entrance of flare at the exposure position and by which editing of more than one document image is possible as required.
Exposure apparatus for use with various types of copiers, printers, presses, etc. commonly employ slit scanning exposure for several advantages it has over one-shot exposure of still image such as, for example, (1) the smallness of an area to be exposed and hence the size of the exposure apparatus, and (2) the need to use a smaller quantity of light from a light source.
An example of the application of a slit scanning exposure apparatus to a copier is shown in FIG. 9. A prior art slit scanning exposure apparatus comprises basically an exposing light source 506 which illuminates a document 504 on a platen 502 as it scans across the underside of the document in the direction indicated by arrow x, a mirror 508 that moves together with the light source 506, mirrors 510 and 512 that move in the same direction as the light source 506 at one half the speed of its movement, a lens unit 514 composed of such elements as imaging lenses, color filters and various types of diaphragm stop, photometric means 516 for performing photometry on reflected light from the document 504 during prescanning or adjustment for white balance, etc., and a shutter 520 which changes the direction of the optical path L in such a way that light is admitted either into the photometric means 516 or onto an exposure plane 518.
In the slit scanning exposure apparatus 500, the document 504 is illuminated with the exposing light source 506 which performs scanning at a predetermined speed in the direction indicated by arrow x. Light reflected from the document 504 (which light is hereinafter referred to as "reflected light") passes through a slit 507 and is reflected, in sequence, by mirror 508 that moves together with the light source 506 and mirrors 510 and 512 that move in the same direction as the light source 506 at one half the speed of its movement. The so reflected light travels over the optical path L and is admitted into the lens unit 514 where it is so adjusted as to be focused in a predetermined exposure position, namely, exposure plane 518 and further adjusted for the quantity and quality of light before it passes through an exposure slit 522 and is focused in the exposure plane 518 so as to scan and expose a light-sensitive material 528 which is being transported by means of two roller pairs 524 and 526 in synchronism with the scan speed of the light source 506.
When the exposure is completed, the light source 506 turns off and the shutter 520 blocks the optical path L by pivoting about a fulcrum 520a to move from the position indicated by a solid line in FIG. 9 to the position indicated by a dashed line.
In the prior art slit scanning exposure apparatus, adjustment of the quality of reflected light which is necessary to adjust the color balance and color densities is accomplished by means of various color filters that are mounted in the light source unit, lens unit or some other unit and which are selectively inserted into the optical path of reflected light. A lens unit having such color filters installed in its interior is shown in FIG. 10. The lens unit which is generally indicated by 514 can be used as the lens unit in the slit scanning exposure apparatus 500 shown in FIG. 9.
The lens unit 514 shown in FIG. 10 comprises the front group 532 and rear group 534 of imaging lenses, a first color filter assembly 536 having a cyan and a yellow filter, a second color filter assembly 538 having a cyan and a magenta filter, a fixed diaphragm stop 540, and a variable diaphragm stop 546 having a pair of plates 542 and 544.
The reflected light travelling in the optical path L has its quantity and quality adjusted by passage through the lens unit 514. Thereafter, the reflected light passes through an exposure slit 522 located in front of the exposure position and is focused in that position to expose a light-sensitive material 528.
To take the first color filter assembly 536 as an example, a cyan filter 550C and a yellow filter 550Y are formed on a colorless and transparent glass plate 550 by evaporation or some other suitable technique and said glass plate is then incorporated into a frame 552. A rack 554 is formed on the frame 552 which engages a motor 560 via gears 556 and 558.
When the motor 560 rotates, the frame 552 of the first color filter assembly 536 is caused to move along the length of exposure slit 522 in the direction indicated by a double-headed arrow, namely, in a direction perpendicular to the scanning direction, and this permits either one of the cyan and yellow filters to be inserted into the optical path L. Stated more specifically, cyan filter 550 C is inserted into the optical path L if the motor 560 rotates clockwise, whereas yellow filter 550Y is inserted into the optical path L if the motor 560 rotates counterclockwise, with the movement of either filter being parallel to the length or longer side of the slit 522. By controlling the amount of motor rotation, the amount in which each filter is inserted into the optical path L is varied to achieve proper adjustment of the reflected light.
The second color filter assembly 538 has the same construction as the first color filter assembly 536 in that a cyan filter 562C and a magenta filter 562M are formed on a transparent glass plate 562.
The prior art slit scanning exposure apparatus 500 shown in FIG. 9 is so constructed that when the imaging lens unit (lens unit 514) is moved along the optical path L, mirrors 510 and 512 are also moved to change the optical path length, with a consequent change in the exposing ratio to permit size reduction or enlargement of the image to be formed. The spot of reflected light focused in the exposure plane 518 has a certain width in the direction in which the light-sensitive material is scanned as indicated by arrow z. This width which is hereinafter sometimes referred to as the "scan width" varies with the specific exposing ratio selected. If the slit 507 in the light source 506 is assumed to have a width of 10 mm, the scan width is 10 mm for the exposing ratio 1:1, 20 mm for the ratio 1:2, and 5 mm for the ratio 1:0.5. Hence, the width of exposure slit 522 located in front of the exposure plane 518 is usually set to about 16-20 mm in a slit scanning exposure apparatus that has a scan width of 10 mm for an exposing ratio of 1:1 and that is capable of exposing at ratios ranging from 1:0.5 to 1:2. However, if the exposure slit 522 has a width of 16 mm, the scan width becomes smaller than said slit width when size-for-size or reduction exposure is to be performed, thereby creating a gap in the exposure slit 522 in either the upper or lower portion or both in the direction of scanning by reflected light. In the presence of such gaps, "flare" such as randomly reflected light from the imaging lens unit or extraneous light will fall on the exposure plane 518 to produce an unsatisfactory image such as an unsharp image or an image with a blurred contour.
Modern versions of slit scanning exposure apparatus are often required to perform a special type of exposure, such as exposing only a selected area of a light-sensitive material with reflected light from a small document and leaving the other areas unexposed, or exposing a light-sensitive material with only the light reflected from part of the image on a document and leaving the other part of the image unprocessed. Following these operation, the unexposed areas are exposed and by performing such multiple exposure, desired portions of more than one image are combined to form a single image. This "editing" procedure is difficult to accomplish with the prior art slit scanning exposure apparatus unless masking or other extra steps are taken.
Including the first color filter assembly 536 and the second color filter assembly 538 used in the lens unit 514 shown in FIG. 10, all of the color filters used to adjust the quality of light in the prior art slit scanning exposure apparatus are so constructed that they are inserted into the optical path in a direction perpendicular to the scanning direction, or in a direction parallel to the slit length, with the reflected light being adjusted in accordance with the amount in which a specific filter is inserted.
As a result of various studies they conducted in order to improve the prior art slit scanning exposure apparatus, the present inventors found that when color filters for adjusting the quality of light were inserted into the optical path L in a direction parallel to the slit length as in the prior art, uneven color formation occurred in the resulting image. As already mentioned, the quality of light is adjusted not only by changing the type of color filter to be inserted into the optical path L but by varying the amount in which it is inserted. Hence, the rays of light emerging from the color filter assembly will unavoidably contain the portion which has passed through the inserted color filter and the portion which has not. The light component which passed through the inserted color filter will have its quality adjusted before it falls on the exposure position to expose the light-sensitive material, whereas the component that has passed through the position where no color filter was inserted will fall, totally unadjusted, on the exposure position to expose the light-sensitive material.
In slit scanning exposure, scanning for exposure is performed along the shorter side of slit, namely, in a direction perpendicular to the direction in which color filters are to be inserted into the optical path. Thus, not all surface of the light-sensitive material can be exposed with properly adjusted light but instead two differently exposed areas will occur on a single light-sensitive material, one area being exposed with properly adjusted light and the other being exposed with yet to be adjusted light. Consequently, the image obtained will not have uniform colors across the surface of the light-sensitive material but suffers the problem of uneven color formation.